Synthetic textile yarn



March 17, 1970 c. w. KIM

SYNTHETIC TEXTILE YARN 2 Sheets-Sheet l Filed July 51, 1968 FIG. 3

m K w S E L R A H C ATTORNEY March 17, 1970 v c. w. KIM 3,500,627

SYNTHETIC TEXTILE YARN Filed July 31, 1968 2 Sheets-Sheet 2 FIG. 9 FIG. IO

CHARLES W. KIM INVENTOR.

MW/QM ATTORNEY United States Patent 3,500,627 SYNTHETIC TEXTILE YARN Charles W. Kim, Heritage Park, Del., assignor to Hercules Incorporated, Wilmington, De]., a corporation of Delaware Filed July 31, 1968, Ser. No. 749,116 Int. Cl. D02g 3/02, 3/06 US. Cl. 57-140 6 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a synthetic textile yarn and particularly to such a yarn formed by the fibrillation of a ribbon of plastic material.

In US. patent application Ser. No. 696,376, there is disclosed and claimed a method and apparatus for fibrillating a ribbon of plastic material to provide a yarn of continuous filaments, with each of the filaments having fibrils extending laterally from the opposed edges thereof. The fibrils impart to the yarn an appearance and hand similar to that of yarn spun in the usual manner from staple fibers. In accordance with the invention of the above noted application, the ribbon from which the yarn is formed is striated, that is, it consists of a plurality of striations or ribs extending lengthwise of the ribbon in parallel and equally-spaced relation and interconnected laterally by webs of reduced thickness relative to the ribs. Upon fibrillation of a highly-oriented ribbon of striated film, splitting occurs along the webs to divide the ribbon into a plurality of individual continuous filaments corresponding generally to the ribs and with fibrils formed from and at the edges of the web portions that extend from the opposite sides of the ribs.

In filaments in accordance with the invention of the above-noted application, since the fibrils are formed from the webs, which are reduced in thickness relative to the ribs, the fibrils are inherently finer in denier than the filaments themselves. The fine denier fibrils have advantages in many applications but they also may be too delicate for use in some fabrics such as carpets that are subject to heavy wear. Fine fibrils of polymeric material are also more readily degraded than fibers of heavier section because they can be more readily penetrated by a degrading force such as ultra-violet light. Fibrils that have a varying cross-section or that have a cross-section that is different from that of the filament itself also are not uniformly dyeable.

The objects of this invention are to provide a yarn consisting of filaments made by the fibrillation of a ribbon of plastic film, which filaments are continuous to provide good tensile properties without requiring a high twist, which adds expense and also compacts the filaments in the yarn thereby reducing bulk and thermal properties. Further objects of this invention are to provide such a yarn in which the filaments have laterally extending fibrils that impart increased bulk and improved thermal, filtering and fluid adhesion properties as well as appearance, which fibrils may have a cross-section generally comparable to that of the filaments themselves whereby the characteristics of the fibrils, such as the dyeability and degradation rate, may also be similar to that of the fila- 3,500,627 Patented Mar. 17, 1970 ments. Further objects of this invention are to provide such a yarn that is uniform throughout and is adapted to be manufactured economically on a commercial basis. Other objects of this invention will be apparent from the following disclosure of the invention.

Briefly, the objects of this invention have been achieved by providing a striated ribbon of plastic material and consisting of a plurality of filament-forming ribs or striations arranged in parallel and equally-spaced relation, and interconnected laterally by a plurality of fibril-forming cross-ribs or striations that are also arranged in parallel and equally-spaced relation but at an acute angle, for example, forty-five degrees, to the filament-forming ribs. Such a ribbon may be formed for example by extruding the filament-forming ribs through a circular arrangement of die holes and the fibril-forming ribs through a concentric arrangement of die holes that are rotated relative to the first series of die holes, or by embossing the ribs upon a film. The ribbon is highly oriented uniaxially in the direction endwise of the filament-forming ribs and is fibrillated by means of a toothed fibrillating device such as that forming the subject matter of the above referred to US. patent application Ser. No. 696,376. The crosssection of the fibrils on the filaments is determined by the cross-section of the fibril-forming ribs of the ribbon and therefore can be made uniform as well as comparable in cross-section to the filaments. The length of the fibrils is also uniform since the fibril-forming ribs generally split about the tooth which becomes engaged at thev junction of the fibril-forming rib and the filament-forming rib.

With the above and other objects in view, the present invention is hereinafter described with reference to the accompanying drawings, in which:

FIG. 1 is a schematic illustration of apparatus for making the plastic ribbon that is to be fibrillated to produce the synthetic filaments with heavy denier fibrils in accordance with this invention.

FIG. 2 is a schematic illustration of apparatus for uniaxially orienting the ribbon formed by the apparatus of FIG. 1.

FIG. 3 is a schematic illustration of apparatus for fibrillating the oriented ribbon formed by the apparatus of FIGS. 1 and 2.

FIG. 4 is a fragmentary sectional view longitudinally of the bar of the apparatus of FIG. 3 and illustrating a portion of the ribbon as it proceeds through the fibrillation process.

FIG. 5 is a fragmentary view in perspective of a portion of the ribbon produced by the apparatus of FIG. 1.

FIG. 6 is a fragmentary view in perspective of a portion of a filament produced by the fibrillation of the ribbon of FIG. 5.

FIGS. 7 and 9 are fragmentary top plan views of ribbons similar to the ribbon of FIG. 5 but embodying modifications of the invention.

FIGS. 8 and 10 are fragmentary top plan views of filaments produced by the fibrillation of the ribbons of FIGS. 7 and 9 respectively.

With reference to the drawings, there is illustrated in FIG. 5 a fragmentary portion of a ribbon 1 of a plastic material suitable for forming a synthetic textile yarn, which material may for example be polypropylene. The ribbon 1 consists of a plurality of filament-forming ribs 2 that are interconnecetd laterally by a plurality of fibrilforming ribs 3. The ribs 2 and the ribs 3 are each arranged in parallel and equally-spaced relation with the ribs 3 arranged at an acute angle, preferably about forty-five degrees, to the ribs 2. As shown, the fibril-forming ribs 3 are about the same in cross-section as the filamentforming ribs 2, although it will be understood that the cross-section thereof may be varied.

The ribbon 1 may be formed for example by an em bossing process such as illustrated in FIG. 1 wherein a film 4 of molten thermoplastic material is extruded from the die openings of an extruder 5 into the nip between an embossing roll 6 and a pressure roll 7. The peripheral surface of the embossing roll 6 is engraved with a pattern defining the desired configuration of the ribbon 1, and the film 4 is forced against the same and thereby formed in accordance with that pattern by the pressure roll 7 which is journaled on a support 8 pivotally mounted as at 9 and biased against the embossing roll by spring means 10. Both the embossing roll 6 and the pressure roll 7 may be chilled so that the embossed film 4a is cooled to its setting temperature while on the roll 6. From the embossing roll 6, the cooled and embossed film 4a is directed to a pair of draw rolls 11 and, from there, the film may be run directly to an orienting operation such as illustrated in FIG. 2 or may be directed to a wind-up device (not shown) to produce a package from which it is unwound at the input of an orienting operation.

The embossed film 4a is uniaxially oriented in the direction longitudinally of the filament-forming ribs 3 by drawing apparatus such as illustrated in FIG. 2. The illustrated apparatus comprises a set of low-speed feed rollers 12 from which the embossed film 4a is directed over a heated drum 13 for heating the same to its orientation temperature, which, for example, with polypropylene may be about 140 C. The embossed film 4a runs about the drum 13, over a pair of guide rolls 14 and 15 which are provided to increase the are over which the film is in contact with the drum, and over a chilled drum 16 to a set of high-speed draw rolls 17. The rolls 17 are operated at a speed that is for example six times the speed of the feed rolls 12 so that the film 4a is elongated at a ratio of 6:1 to provide the oriented film 4b.

For manufacturing purposes, the film 4 is preferably extruded in a width that is many times the width of ribbon 1, and is subsequently slit into a plurality of the ribbons 1 by a cutter (not shown). Such slitting may be done at any convenient point in the process, such as between the embossing roll 6 and draw rolls 11 or before or after the orientation of the embossed ribbon 4a, or, preferably, at the input of the fibrillation operation hereinafter described.

Fibrillation of the oriented film 4b is effected by apparatus such as illustrated in FIG. 3. The illustrated apparatus is similar to that forming the subject matter of the above noted U.S. patent application Ser. No. 696,376 and comprises a bar 18 having an axial shaft 19 journaled in brackets 20 and 21. Rotation is imparted to the bar 18 by a belt 22 entrained about a pulley 23 fixed upon the end of the shaft 19. The ribbon 1 is fed across the bar 18 in the direction endwise of the filament-forming ribs 2 by a pair of nip rolls 24 and a pair of draw rolls 25 that operate at a speed slightly faster than the nip rolls 24 to impose a tension onthe film. The rolls 24 and 25 are disposed with the axis thereof substantially parallel to the axis of the bar 18 whereby the ribbon 1 is fed substantially flat across the bar 18. The rolls 24 and 25 are also disposed with the axis thereof substantially at the level of or lower than the axis of the bar 18 so that the ribbon 1 isangled over the bar 18 to obtain a desired arc of contact between the ribbon 1 and the bar.

In its illustrated form, the bar 18 has a cross-section in the shape of an equilateral triangle to provide three edges 26. The edges 26 are formed with teeth 27 which, when the bar 18 is rotated relative to the ribbon 1, enter individually between a pair of filament-forming ribs 2 and engage the fibril-forming ribs 3. With the bar 18 rotating at a high speed relative to the speed at which the ribbon 1 is advanced, the teeth move rapidly into engagement with or impact against the fibril-forming ribs 3. Inasmuch as a rib 3 is at an angle relative to the path of the respective tooth 27, the tooth tends to run along the rib 3 unil it is lodged at the converging intersection between the ribs 3 and the filament-formnig ribs 2. Continued advance of a tooth relative to the ribbon 1 imposes an increasing tension upon the respective rib 3 until it breaks. Inasmuch as the fibril-forming rib 3 is, as hereinafter discussed, the weaker of the two ribs and because of the snubbing action of the rib 3 about the tooth 27, the break generally occurs in the rib 3 about the tooth 27 which, since the tooth is then lodged at the junction of the ribs 2 and 3, means that the break occurs generally at the juncture of the rib 3 with the filament-forming rib 2.

When the gauge of the teeth 27 is sufiiciently close to that of the ribs 2, and the number of edges 26 or the speed of the bar relative to the speed of the ribbon 1 is sufficiently high, there will be a tooth 27 inserted into each space bounded by the ribs 2 and 3 and each of the ribs 3 will be broken between each pair of ribs 2. The resulting product, a section of one filament of which is illustrated in FIG. 6, comprises separate individual filaments 30 that correspond generally to the filament-forming ribs 2, each of which filaments 30 has fibrils 31 that correspond generally to the section of the fibril-forming ribs 3 between two adjacent ribs 2. Like the ribs 3, the fibrils 31 extend from the filament 30 at an acute angle although it may be at an angle that was reduced somewhat during the drawing operation from the angle at the original embossing. Each of the fibrils 31 diverges relative to the filament 30 to a free end 32 which is a broken end at which the rib 3 Was broken by the tooth 27. The remaining portion of the fibril-forming rib 3 remains as a stub 33 on the opposed edge of the adjacent filament. With a parallel arrangement and thus a uniform angling of the ribs 3, the length of the fibrils 31 is determined essentially by the lateral spacing of the filament-forming ribs 2. A uniform spacing of the fibril-forming ribs 3 along the ribs 2 is produced by the uniform spacing of the fibrils 31 along the filament 30.

When a plurality of the filament 30 are combined into a yarn, the normal twisting of the filaments about their axes disperses the fibrils 31 in a generally spiral manner about the axis of the filament 30. The fibrils 31 tend to hold the adjacent filaments 30 in spaced relation in a positive manner in the yarn, which increases the bulk of the yarn. The stiffness of the fibrils laterally of the filament is enhanced by the fact that the fibrils 31 have a significant cross-section and also have a normal angle relative to the filaments. At the same time, the fibrils span the space between adjacent filaments 30 in the yarn to improve the thermal and filtering characteristics of the yarn. The uniformity of the fibrils 31 along the filaments 30 produces a yarn that is uniform in appearance and in physical characteristics. With fibrils 31 that have a cross-section that is substantially uniform and matches that of the filaments 30, the filaments 30 and fibrils 31 are more uniformly dyeable. Because the fibrils are formed primarily by embossing and not by tearing the same from the filaments and are oriented as separate elements, the axis of orientation thereof is disposed relative to the axis of orientation of the filaments at an angle corresponding to the angle of the fibrils and there are no natural tear lines or natural lines of weakness permitting tearing the fibrils loose from the filaments, and the resulting product is therefore quite strong anddurable. A further advantage of the yarn in accordance with this invention is that the interlocking of the fibrils tends to bind the filaments into a coherent yarn with a high twist which tends to reduce the bulk as well as the insulation properties of the yarn.

A significant feature of this invention is that the fibrilforming ribs 3 may be somewhat weaker than the filament-forming ribs 2 although they may be substantially the same in cross-section. With the fibril-forming ribs 3 arranged at an acute angle relative to the filament-forming ribs 2, and since the filament-forming ribs 2 are free to move closer together when they are drawn endwise during orientation, the fibril-forming ribs 3 become aligned in a more parallel relation relative to the rib 2 during drawing. Thus the length of the fibril-forming ribs 3 is greater than the length of the filament-forming ribs 2 in the direction endwise of the ribs 2, with the result that the ribs 3 are drawn at a ratio that is proportionally reduced relative to that of the ribs 2. Because of the lower level of orientation, and despite the fact that the crosssection may be comparable, the ribs 3 have reduced tensile strength relative to the ribs 2. In order to achieve comparable cross-sections in the ribs 2 and 3 of the ribbon 1 after it is oriented, the ribs 2 in the original film 4 may be heavier by an amount corresponding to the greater reduction in cross-section because of the greater draw ratio.

While the oriented film 4b in the above description is produced by embossing an extruded film, similar results can be achieved by other known processes such as a pair of relatively movable concentric dies, each having a series of die holes for extruding a plurality of individual filaments. In this case, one of the dies extrudes a cylindrical sheet of individual filaments that is drawn endwise relative to the die while the other die extrudes a concentric sheet of individual filaments that are rotated spirally relative to the first sheet with each filament of the second sheet melt-joined at the crossing point to each filament of the first sheet. The thickness at the crossing points of the ribs 2 and 3 is generally equal to the combined thickness of the ribs 2 and 3, and the ribs may be generally round in cross-section. The round cross-section is to be distinguished from an embossed film formed by the apparatus of FIG. 1 in which the ribs are generally semicircular in cross-secti0n and the thickness at the crossing point is not increased. However, with an embossing apparatus in which the embossing roll 6 impresses only one set of ribs such as the ribs 2 on the film and the other set of ribs is formed by a second embossing roll that is substituted for the pressure roll 7, the crossing points of the ribs would be doubled in thickness.

Generally, the manner in which the film 4 is formed does not materially affect the fibrillation or the resulting product although it may affect the orientation level of the fibrils or the presence of fine side hairs on the filaments 30 and fibrils 31. With a film 4 having increased thickness at the crossing point, the elongation of the filamentforming ribs 2 within the width of the crossing point does not effect any elongation of the fibril-forming ribs 3 so that there is no orientation of the ribs 3 as this portion of the rib 2 is drawn. The resulting orientation level of the ribs 3 is correspondingly lower. Accordingly, the tensile strength of the ribs 3 is also lower while the increased thickness of the rib 2 at the juncture renders it stronger so that the strength differential between the ribs 2 and 3 is increased and there is thus additional assurance that the break will occur in the rib 3. The fine side hairs are produced by a thin film or web of the material within the space bounded by the ribs 2 and 3 formed during the embossing operation. This Web is split during fibrillation into fine side hairs that adhere to the filaments 30 and fibrils 31.

The angle of the fibril-forming ribs 3 relative to the filament-forming ribs 2 in the ribbon 1 is preferably about forty-five degrees but this angle is not critical. The critical feature is that the draw ratio of the fibril-forming ribs 3 be sufiiciently high that the elongation required to break the same is reduced to a relatively low figure, for example, ten to twenty-five percent. With a relatively high elongation, the rib 3 may have sufficient elastic yield to accommodate the relative movement between the tooth and the rib without breaking. In order to achieve the required elongation properties, the ribs 3 are angled relative to ribs 2 at an angle in excess of about fifteen or twenty degrees and less than about seventy or seventy-five degrees.

In considering the effect of the angle between the ribs 2 and 3 upon the orientation level achieved in the ribs, it may be assumed for purposes of comparison that two adjacent filament-forming ribs 2 are free to move into sideby-side abutting relation when they are drawn endwise. Thus, when drawn, there is no elongation of the fibrilforming ribs 3 until the ribs 2 are drawn to a length equal to the segment of the rib 3 between the two ribs, that is until they are drawn by an amount determined by the sine of the angle between them. Thereafter, the ribs 2 and 3 are drawn uniformly but the draw ratios of them vary because of the diiference in the undrawn or original length of the fibril-forming rib 3 relative to the undrawn length of the filament-forming rib 2. If the ribs 3 were at ninety degrees to the ribs 2, the length component of the rib 3 in the direction endwise of the rib 2 is zero. When such a ribbon is drawn, the opposite ends of a segment of a rib 3 advances in unison with the result that there is no elongation of the rib segment and it merely buckles as the spacing between the two adjacent ribs 2 is reduced. When the angle is increased, the length component of the segment of the rib 3 in the direction endwise of the ribs 2 is increased as a sine function. By way of example, with a draw ratio of six for the ribs 2, the arrangement of the ribs 3 at any angle less than about ten degrees (that is, angle having a sine of less than 0.167) would produce no drawing of the ribs 3 since the entire elongation of the rib 2 would be required to align the rib 3 in a parallel relation with respect thereto. At an angle of about twenty degrees, the section of the rib 3 is about three times as long as the length component thereof in the direction endwise of the rib 2, so that a draw ratio of six for the rib 2 produces a draw ratio of about two in the rib 3. Polypropylene filaments oriented at a draw ratio of two has a break elongation of about 300 percent and is therefore difiicult to break without excessive elongation. At forty-five degrees, the draw ratio of the rib 3 is about four when the rib 2 is drawn at a ratio of six. At seventy degrees, drawing the rib 2 at a ratio of six will draw the rib 3 at a ratio of roughly five and one-half. Polypropylene filaments oriented at such a draw ratio have about percent of the tensile strength of the same filaments oriented at a ratio of about six and with a strength differential this small, breaking will not occur uniformly at the rib 3.

In FIGS. 7 and 8, there is illustrated a modification of the invention in which the ribbon 1a includes filamentforming ribs 2a and two sets of fibril-forming ribs 3a and 3b which are oppositely angled relative to the ribs 2a. The filaments produced by the fibrillation of the ribbon 1a is illustrated in FIG. 8 and comprises a filament 30a having fibrils 31a and 31!) which correspond respectively to the ribs 3a and 3b. Some of the fibrils 31a and 31b terminate in free ends 32a and 32b while others remain joined as at 310 which correspond to the crossing points 3c in the ribbon 1a. One of the advantages of a yarn of this type is the increased tendency for the fibrils to entangle and thus to form a more coherent yarn with less twisting.

In FIGS. 9 and 10, there is illustrated a further modification of the invention in which a ribbon 1d includes filament-forming ribs 2d and fibril-forming ribs 2e which are arranged in a herring bone pattern rather than in straight lines. Upon fibrillation of the ribbon 1d, there are produced two different types of filaments, that is, a filament 30d having fibrils 31d and a filament 30c having stub ends 332.

While the present invention is specifically directed to forming relatively heavy denier fibrils, that is, fibrils that are roughly comparable in cross-section to the filaments, it will be apparent that a relatively wide range of crosssections can be produced. Many of the advantages of the invention, such as uniformity and durability, can be achieved with filaments having fibrils that are smaller in cross'section than the filaments as well as with those that are substantially equal to or larger than the filaments.

'6. A method of making a synthetic yarn comprising:

forming a ribbon ofplastic material with a plurality of filament-forming ribs having a substantially common cross-section and arranged in spaced parallel relation and a plurality of fibril-forming ribs having a substantially common cross-section and arranged in spaced parallel relation and disposed at an acute angle to said filament-forming ribs,

orienting said ribbon uniaxially in the direction endwise of said filament-forming ribs whereby both said filament-forming ribs and said fibril-forming ribs are oriented longitudinally with the orientation of said filament-forming ribs being at a higher ratio than the orientation of said fibril-forming ribs,

and fibrillating said ribbon by severing said fibrilforming ribs to form filaments corresponding to said filament-forming ribs and having fibrils corresponding to said fibril-forming ribs extending laterally therefrom.

The filaments such as the filaments 30 are herein referred to as continuous but it will be apparent that they can in the usual manner be chopped into staple length and used as staple.

What I claim and desire to protect by Letters Patent is:

1. A synthetic yarn of plastic material comprising a plurality of uniaxially oriented filaments that are substantially uniform in cross-section along the length thereof, and fibrils disposed at pre-determined intervals along each of said filaments, said fibrils having a common crosssection and a substantially uniform length and extending from said filaments uniformly at an acute angle, said fibrils being oriented uniaxially in the direction endwise thereof at a level lower than the orientation level of said filaments whereby the axis of orientation of said fibrils intersects the axis of orientation of said filament at an angle corresponding substantially to the angle of said fibrils relative to said filaments.

2. A synthetic yarn in accordance with claim 1 in which the angle of said fibrils relative to said filaments is between about twenty and seventy degrees.

3. A synthetic yarn in accordance with claim 2 in which the angle of said fibrils relative to said filaments is about forty-five degrees.

4. A synthetic yarn in accordance with claim 1 in which the cross-section of said fibrils is substantially comparable to the cross-section of said filaments.

5. A synthetic yarn in accordance with claim 1 in which said fibrils extend from one edge of the filaments and terminate in a free edge, and there is a short fibril section corresponding in cross-section to said fibril and extending from said filament on the opposite side from said fibril and in alignment with said fibril.

References Cited UNITED STATES PATENTS 8/ 1965 Scragg 57140 XR 9/1966 Scragg 57--140 2/ 1967 Greene 28-1 4/ 1968 Matsui et al 281 XR FOREIGN PATENTS 1/ 1966 France.

30 DONALD 'E. WATK'INS, Primary Examiner US. Cl. X.R. 

